All the Operators
Precedence
• An operator with higher precedence is done earlier
(prededes) one with lower precedence
– A higher precedence is indicated with a lower number;
zero is the highest precedence
• Most of the time, operators with equal precedence
are done left to right
– Examples:
3 + 4 * 5 gives 23
10 - 5 - 2 gives 3
• Exceptions: unary operators, casts, assignment
operators, the ternary operator: all done right to left
Postfix operators
• Postfix operators have the highest precedence
(parameters) Parameter lists
[ ] Brackets indicate indexing into an array
.
Accesses methods and variables
expr++, expr-- Postincrement, postdecrement
Unary prefix operators
• Unary prefix operators have the next highest
precedence:
++expr Preincrement
--expr Predecrement
+ - Unary plus and unary minus
!
Logical negation (not)
~ Bitwise complement (invert every bit)
Object creation and casting
new
Create a new instance of a class
(type)
Cast (convert) to the given type
• Slides are in order of decreasing precedence
– Higher precedence means “more tightly bound”
– The lowest precedence operator is the “main” operator
in an expression
Multiplicative operators
*
Multiply
/
Divide
%
Modulus
• These all have the same precedence
Additive operators
+
-
Add
Subtract
Shift operators
<<
Left shift, end off
– For small integers, this is equivalent to multiplying by a
power of two
– Example: 100 << 3 gives 800
>>
Right shift with sign extension
– For small integers, this is equivalent to an integer divide
by a power of two
– Example: 100 >> 2 gives 25
>>>
Right shift with zero fill
– Does not make sense for numbers
Relational operators
<
<=
>
>=
Less than
Less than or equal to
Greater than
Greater than or equal to
instanceof Left operand is an object whose type (class
or interface) is the right operand
• These all have the same precedence, and it is higher than
equality/inequality tests
Equality and inequality
==
Test if equal
– For primitive types, tests if the values are equal
– For objects, tests if both sides refer to the same object
!=
Test if not equal
– For primitive types, tests if the values are unequal
– For objects, tests if the sides refer to different objects
• Reminder: these tests should not be used on floatingpoint numbers (float or double)
AND
&
AND
– For integral types, ANDs each corresponding pair of
bits
•0&
0&
1&
1&
0 == 0
1 == 0
0 == 0
1 == 1
– For booleans, performs the logical AND operation
• Boolean & is like &&, but both operands are
evaluated, even if it is possible to decide the result
from the left operand alone
Exclusive OR
^
XOR
– For integral types, XORs each corresponding pair of
bits
•0^0
0^1
1^0
1^1
== 0
== 1
== 1
== 0
– For booleans, performs the logical XOR operation
• a ^ b is true if either a is true or b is true, but not both
• There is no ^^ operation
OR
|
OR
– For integral types, ORs each corresponding pair of bits
•0|
0|
1|
1|
0 == 0
1 == 1
0 == 1
1 == 1
– For booleans, performs the logical OR operation
• Boolean | is like ||, but both operands are
evaluated, even if it is possible to decide the result
from the left operand alone
The ternary operator
• boolean-expr ? expression-1 : expression-2
• This is like if-then-else for values rather than for
statements
• If the boolean-expr evaluates to true, the result is
expression-1, else it is expression-2
• Example: max = a > b ? a : b ; sets the variable max to
the larger of a and b
• expression-1 and expression-2 need not be the same type, but
either result must be useable
• The ternary operator is right associative!
– To avoid confusion, use parentheses if your expression has more than
one ternary operator
The assignment operators I
• The assignment operators have the lowest
precedence
– Assignment is an operation
– Assignment is right associative
a = b = c = 7.5 * w;
• assigns 7.5*w to c, then assigns c to b, then assigns b to a – if all
these assignments are legal
• Example:
– if ((line = reader.newLine()) == null) { ... }
The assignment operators II
• There are a lot of assignment operations besides =
• variable += expression means the same as
variable = variable + expression
• variable -= expression means the same as
variable = variable - expression
• variable *= expression means the same as
variable = variable * expression
• variable /= expression means the same as
variable = variable / expression
The assignment operators III
• variable %= expression means the same as
variable = variable % expression
• variable <<= expression means the same as
variable = variable << expression
• variable >>= expression means the same as
variable = variable >> expression
• variable >>>= expression means the same as
variable = variable >>> expression
The assignment operators IV
• variable &= expression means the same as
variable = variable & expression
• variable |= expression means the same as
variable = variable | expression
• variable ^= expression means the same as
variable = variable ^ expression
What you need to know
• You should understand what each operator does
• Parameter lists, array indexing, casting, postfix ++ and --, and
the dot operator are done first
– In particular, a cast refers to the one following entity, so to cast the
result of an expression you need extra parentheses
– Example 1: variable = (type)(expression);
– Example 2: variable = ((type)variable).method();
• In arithmetic, the unary operators + and – are done first, then
multiplication and division, then addition and subtraction
• All assignment operators are done last
• For anything else, it’s a good idea to use parentheses anyway
(even if you remember the order of precedence, other people
won’t)
The End